Sealing element for a gas turbine, a gas turbine including said sealing element and method for cooling said sealing element

ABSTRACT

A sealing element for a gas turbine, which is provided with at least one rotor ring and at least a plurality of rotor blades radially arranged about the rotor ring and having an end portion fixed to the rotor ring, is provided with a wall, which is adapted to be coupled to the rotor ring and to at least one rotor blade, has an external face adapted to be arranged in contact with a hot working fluid in the gas turbine and an internal face adapted to be arranged in contact with a cooling fluid of the gas turbine, and a gap, which is adapted to be travelled through by the cooling fluid.

The present invention relates to a sealing element for a gas turbine, toa gas turbine including said sealing element and to a method for coolingsaid sealing element.

BACKGROUND OF THE INVENTION

Gas turbines of known type generally include a rotating shaft, extendingalong a longitudinal axis, with a plurality of rotor rings connectedthereto, each of which is centered on the longitudinal axis. Each rotorring is coupled to a plurality of rotor blades radially arranged aboutthe rotor ring.

Specifically, each rotor ring is provided with a plurality ofessentially equally spaced seats, which axially extend along theperipheral edge of the rotor ring. Each seat is adapted to be engaged byan end portion of a corresponding rotor blade by means of an axiallysliding prismatic coupling. This type of coupling between the blade andthe rotor ring ensures, when the turbine is running, an appropriatefastening of the blade in a radial direction, but allows the blade endportion to be displaced in the axial direction. Therefore, the axialmovement of the end portions of the blades must be prevented. Such anobject is generally reached by using sealing elements, which arecircumferentially arranged side-by-side to essentially form a sealingring and which are fixed to the rotor ring and to one or more rotorblades, on one or both of the annular faces of the rotor ring.

The sealing elements further contribute to correctly cool the rotorblades because they protect the end portions of the rotor blades fromthe hot working fluid in the gas turbine. Each sealing element indeedincludes a wall having an external face in contact with the hot workingfluid in the gas turbine and an internal face in contact with thecooling fluid of the gas turbine. However, the sealing elements areoften subjected to overheating, because the contact with the coolingfluid along the internal face is not sufficient to ensure an adequatecooling of the whole sealing element. Specifically, the sealing elementis provided with an upper edge adapted to be coupled to the rotor blade,which is particularly subject to overheating because it is subjected toa fairy high heat load due to its position close to the flow area of thehot working fluid. Such an upper edge reaches very high temperatures andundergoes plastic deformations due to the overheating and to thesimultaneous action of the centrifugal force which cause a sort ofwelding of the sealing element onto the rotor blade. This implies greatdifficulties, for example, during the operations of disassembling thesealing elements, because very often it is necessary to resort tooperations which damage the sealing elements and risk damaging the rotorblade as well.

SUMMARY OF THE INVENTION

It is an object of the present invention to make a sealing element whichis free from the prior art drawbacks highlighted herein; specifically,it is an object of the invention to make a sealing element shaped so asto ensure an appropriate cooling of the upper edge while being easy andcost effective to be made.

In accordance with these objects, the present invention relates to asealing element for a gas turbine; the gas turbine including at leastone rotor ring and at least a plurality of rotor blades radiallyarranged about the rotor ring and having an end portion fixed to therotor ring; the sealing element including a wall which is coupled to therotor ring and to at least one rotor blade and is provided with anexternal face in contact with a hot working fluid in the gas turbine andwith an internal face in contact with a cooling fluid of the gasturbine;

the sealing element being characterized in that the wall has a gap whichis adapted to be travelled through by the cooling fluid.

It is a further object of the present invention to make an efficient gasturbine. In accordance with such objects, the present invention furtherrelates to a gas turbine including at least one rotor ring and at leasta plurality of rotor blades radially arranged about the rotor ring andhaving an end portion fixed to the rotor ring; the gas turbine beingcharacterized in that it includes at least one sealing element asclaimed in the attached claims.

It is a further object of the present invention to provide a simple andeffective method for cooling a sealing element of a gas turbine. Inaccordance with these objects, the present invention relates to a methodfor cooling a sealing element for a gas turbine; the gas turbineincluding at least one rotor ring and at least a plurality of rotorblades radially arranged about the rotor ring and having an end portionfixed to the rotor ring; the sealing element including a wall, which isadapted to be coupled to the rotor ring and at least one rotor blade andis provided with an external face adapted to be arranged in contact witha hot working fluid in the gas turbine and with an internal face adaptedto be arranged in contact with a cooling fluid in the gas turbine; themethod being characterized in that it includes the step of conveying thecooling fluid into a gap of the wall of the sealing element.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and advantages of the present invention will beapparent from the following description of a non-limitative embodimentthereof, with reference to the figures in the accompanying drawings, inwhich:

FIG. 1 is a perspective view, with parts in section and parts removedfor clarity, of a first detail of the gas turbine according to thepresent invention;

FIG. 2 is a perspective view, with parts removed for clarity, of asecond detail of the gas turbine according to the present invention;

FIG. 3 is a perspective view of a sealing element according to thepresent invention;

FIG. 4 is a perspective view, with parts removed for clarity, of adetail of a sealing element made according to a different embodiment ofthe present invention.

DETAILED DESCRIPTION OF THE INVENTION

In FIG. 1, reference numeral 1 indicates a portion of a gas turbineincluding a rotor ring 2 (only partially shown), which is centered on alongitudinal axis (not shown in the accompanying figures) and is coupledto a plurality of rotor blades 3 radially arranged about the rotor ring2.

The rotor ring 2 is provided with a plurality of essentially equallyspaced seats 5, which axially extend along a peripheral edge 6 of therotor ring 2. Each seat 5 is adapted to be engaged by an end portion 7of a corresponding rotor blade 3 by means of a sliding prismaticcoupling; specifically, each seat 5 has two side walls 8, respectivelyprovided with three axial undercuts 9 adapted to prevent the movement ofthe end portion 7 of the blade 3 in the radial direction when theturbine 1 is running.

Each blade 3 includes, as mentioned above, an end portion 7, a platform11, integrally coupled to the end portion 7, and an elongated main body12, which extends from the platform 11 at the opposite side with respectto the end portion 7.

The end portion 7 of each blade 3 may be inserted in the correspondingseat 5 of the rotor ring 2 in a direction parallel to the axis of therotor ring 2. Specifically, the end portion 7 has a shape essentiallycomplementary to the shape of the corresponding seat 5 of the rotor ring2, but has a lower radial height than the radial height of the seat 5 sothat, when the seat 5 is engaged, the end portion 7 forms a channel 14for the passage of a cooling fluid, preferably air bled from thecompressor (not shown) of the gas turbine 1.

The end portion 7 of each blade 3 is further provided with one or moreinternal channels (not shown in the accompanying figures), which facethe channel 14 and provide to cool the end portion 7 itself and to feeda complex system of cooling channels 15 (only one of which is partiallyshown in FIG. 1) of the main body 12.

The platform 11 of each blade 3 has two axially opposite peripheralportions 19, which axially exceed with respect to the end portion 7. Aperipheral portion 19 of the platform 11 is provided, on the side facingthe end portion 7, with a circumferential groove 20. A variant (notshown) of the present invention provides for both peripheral portions 19having a circumferential groove 20, on the side facing the end portion7.

The main body 12 of each blade 3 includes a tip (not shown forsimplicity in the accompanying figures), opposite to the end portion 7,a leading edge 16 and a trailing edge 17.

The gas turbine 1 further includes a plurality of sealing elements 22(only one of which is shown in FIG. 1 for simplicity), which are adaptedto be coupled to the rotor ring 2 and to the blades 3 and arrangedside-by-side in the circumferential direction to contribute to fastenthe end portions 7 of the blades 3 in the axial direction and tocorrectly cool the end portions 7 of the blades 3. In the non-limitativeexample shown in the accompanying figures, the sealing elements 22 arearranged side-by-side in the circumferential direction on only oneannular face of the rotor ring 2. A variant (not shown) of the presentinvention provides for the sealing elements 22 being arrangedside-by-side in the circumferential direction on both annular faces ofthe rotor ring 2.

With reference to FIGS. 1 and 2, each sealing element 22 includes anessentially rectangle-shaped wall 23, which has an external face 24adapted to be arranged in use in contact with the hot working fluid inthe turbine and an internal face 25 adapted to be arranged in use incontact with the cooling fluid from the channel 14.

With reference to FIG. 2, the wall 23 has an upper edge 26 adapted toengage the circumferential groove 20 of the platform 11 of at least oneblade 3; in the example of the accompanying figures, the sealing element22 is arranged straddled on two blades 3 and therefore the upper edge 26engages the circumferential groove 20 of a blade 3 and thecircumferential groove 20 of the adjacent blade 3.

The wall 23 has a lower edge 27 adapted to engage a correspondingportion of a circumferential seat 28 made in the rotor ring 2.

With reference to FIGS. 2 and 3, the wall 23 includes a gap 29, which istravelled through by the cooling fluid from the channel 14 and flowingin the space between the sealing element 22 and the end portion 7 of theblade 3 facing thereto.

Specifically, the gap 29 communicates with the hot working fluid in thegas turbine through one or more outlets 30 (FIGS. 1 and 3) made in theexternal face 24 close to the upper edge 26 and with the cooling fluidthrough one or more inlets 31 (FIG. 3) made in the internal face 25close to the upper edge 26.

The inlets 31 and the outlets 30 are reciprocally and circumferentiallyoffset.

In the non-limiting example described and illustrated herein, theoutlets 30 are three holes, which are essentially adjacent and circularin section, while the inlets 31 are two holes, which are essentiallyadjacent and circular in section. It is understood that the numberand/or shape and/or size of the inlets 31 which feed the gap 29 may bevaried to calibrate the amount of cooling fluid as required (highperforming machines, more or less thermally loaded turbine stages,etc.). Similarly, the number and/or shape and/or size of the outlets 30may also be varied as required.

In the non-limiting example described and illustrated herein, the gap 29is open at the upper edge 26 of the wall 23 and deeply extends into thewall 23 for a length preferably equal to about 1/25 of the total lengthof the wall 23, between the upper edge 26 and the lower edge 27.

Each sealing element 22 further includes a plurality of ribs 33 and ablocking element 34.

The ribs 33 extend from the internal face 25 of the wall 23, essentiallyfor the entire length of the wall 23 between the upper edge 26 and thelower edge 27, are parallel to each other, and essentially orthogonal tothe upper edge 26 of the wall 23. The ribs 33 act to structurallystiffen the sealing element 22 so as to make it sufficiently strong tosupport the action of the centrifugal force and the pressure differenceto which the sealing element 22 is subjected when the gas turbine 1 isrunning.

With reference to FIG. 1, the blocking element 34 is essentially anelongated foil, integrally connected to the wall 23 of the sealingelement 22 and having a tip-shaped end 36 adapted to be arranged in acorresponding seat 37. The shape of the seat 37 is complementary to theend 36 and is defined by the peripheral portions 19 of the platforms 11of two adjacent blades 3. Specifically, the blocking element 34 isC-folded to allow the passage of the blocking element 34 through twoessentially adjacent slots 38, of the external face 24 of the wall 23.The blocking element 34 prevents the movement of the sealing element 22in the circumferential direction.

FIG. 4 shows a variant of the sealing element 22, according to which thegap 29 is provided with a plurality of fins 39 which protrude from twocorresponding internal faces 40 parallel to the internal face 25 of thewall 23 for increasing the heat exchange surface.

In the example shown in FIG. 4, the fins 39 are arranged transversallyto the corresponding faces 40.

Once all the sealing elements 22 have been coupled to the correspondingblades 3 and to the rotor ring 2, in use, the cooling fluid from thechannels 14 of each blade 3 enters the gap 29 of each sealing element 22through the inlets 31 and exits from the gap 29 through the outlets 30.The cooling fluid determines a cooling by convection of the area closeto the upper edge 26 when passing inside the gap 29 (possibly increasedby the presence of the fins 39) and a cooling by convection of theplatform 11 of the rotor blades 3 and of the seat 37 of the blockingelement 34 exiting from the outlets 30.

The present invention has the following advantages.

Firstly, in virtue of the particular shape of the sealing element 22according to the present invention, the disassembly interventions of therotor blades 3 are easier, faster and most cost-effective because thecorrect cooling of the upper edge 26 of the sealing element 22eliminates the problems related to plastic deformations of the upperedge 26.

Furthermore, in virtue of the sealing element 22 according to thepresent invention, it is possible to increase the operating temperatureof the working fluid in the gas turbine 1 and, accordingly, increase theperformance of the entire gas turbine 1.

Additionally, the production costs of the sealing element 22 may bereduced in virtue of the good cooling of the upper edge 26, reached bymeans of the particular shape of the sealing element 22, which no longerimposes the use of materials having high mechanical features.

Furthermore, the risks of failure of the whole gas turbine 1 caused bethe sealing element 22 exiting from its seat due to thermal-mechanicaldeformation is minimized. This further determines an increase of thetime span between a maintenance intervention and the next of the sealingelements 22.

Finally, the sealing element 22 according to the present invention isadapted to be installed on any type of gas turbine, also on previouslyinstalled gas turbines.

It is finally apparent that changes and variations may be made to thesealing element, to the gas turbine and to the method for cooling thesealing element described herein, without departing from the scope ofthe appended claims.

1. A sealing element (22) for a gas turbine (1); the gas turbine (1)including at least one rotor ring (2) and at least a plurality of rotorblades (3) radially arranged about the rotor ring (2) and having an endportion (7) fixed to the rotor ring (2); the sealing element (22)including a wall (23), which is adapted to be coupled to the rotor ring(2) and to at least one rotor blade (3) and is provided with an externalface (24) adapted to be arranged in contact with a hot working fluid inthe gas turbine (1) and with an internal face (25) adapted to bearranged in contact with a cooling fluid of the gas turbine (1); thesealing element (22) being characterized in that the wall (23) has a gap(29), which is adapted to be travelled through by the cooling fluid. 2.An element according to claim 1, characterized in that the wall (23) hasan upper edge (26) adapted to engage a corresponding circumferentialgroove (20) of a rotor blade (3); the gap (29) substantially extendingclose to the upper edge (26).
 3. An element according to claim 1,characterized in that the wall (23) has a lower edge (27) adapted toengage a circumferential seat (28) made in the rotor ring (2).
 4. Anelement according to claim 2, characterized in that the internal face(25) of the wall (23) is provided with at least one inlet (31) forfeeding the gap (29) with the cooling fluid of the gas turbine (1). 5.An element according to claim 4, characterized in that the inlet (31) isarranged on the internal face (25), essentially close to the upper edge(26).
 6. An element according to claim 4, characterized in that theexternal face (24) of the wall (23) is provided with at least one outlet(30) for communicating the gap (29) with the hot working fluid of thegas turbine (1).
 7. An element according to claim 6, characterized inthat the outlet (30) is arranged on the external face (24), essentiallyclose to the upper edge (26).
 8. An element according to claim 6,characterized in that the inlet (31) and the outlet (30) arecircumferentially offset.
 9. An element according to claim 2,characterized in that the gap (29) is open at the upper edge (26) of thewall (23).
 10. An element according to claim 3, characterized in thatthe gap (29) deeply extends into the wall (23) for a length equal toabout 1/25 of the entire length of the wall (23) between the upper edge(26) and the lower edge (27).
 11. An element according to claim 3,characterized in that it includes a plurality of ribs (33), which extendfrom the internal face (25) of the wall (23).
 12. An element accordingto claim 11, characterized in that the ribs (33) are parallel to eachother and essentially orthogonal to the upper edge (26) of the wall(23); the ribs (33) essentially extending for the entire length of thewall (23) between the upper edge (26) and the lower edge (27).
 13. Anelement according to claim 2, characterized in that it includes ablocking element (34) integrally connected to the wall (23) of thesealing element (22) and having a tip-shaped end (36), adapted to bearranged in a corresponding seat (37) defined by two adjacent rotorblades (3).
 14. An element according to claim 2, characterized in thatthe gap (29) is provided with a plurality of fins (39) which extend fromtwo corresponding internal faces (40) of the gap (29).
 15. An elementaccording to claim 14, characterized in that the fins (39) aretransversally arranged with respect to the corresponding faces (40). 16.A gas turbine including at least one rotor ring (2) and at least aplurality of rotor blades (3) radially arranged about the rotor ring (2)and having an end portion (7) fixed to the rotor ring (2); the gasturbine (1) being characterized in that it includes at least one sealingelement (22) according to claim
 1. 17. A method for cooling a sealingelement (22) for a gas turbine (1); the gas turbine (1) including atleast one rotor ring (2) and at least a plurality of rotor blades (3)radially arranged about the rotor ring (2) and having an end portion (7)fixed to the rotor ring (2); the sealing element (22) including a wall(23), which is adapted to be coupled to the rotor ring (2) and to atleast one rotor blade (3) and is provided with an external face (24)adapted to be arranged in contact with a hot working fluid in the gasturbine (1) and with an internal face (25) adapted to be arranged incontact with a cooling fluid of the gas turbine (1); the method beingcharacterized in that it includes the step of conveying the coolingfluid into a gap (29) of the wall (23) of the sealing element (22).